From: Kaitao Cheng <[email protected]> KF_ARG_PTR_TO_LIST_NODE normally requires an owning reference (PTR_TO_BTF_ID | MEM_ALLOC with ref_obj_id). Introduce the __nonown_allowed annotation on selected list-node arguments so non-owning references with ref_obj_id==0 are accepted as well.
This patch only adds the generic verifier support and documents the annotation. Later patches in the series will apply it to bpf_list_add /del(), and bpf_list_is_first/last(), allowing bpf_list_front/back() results to be used as the insertion point, deletion target, or query target for those kfuncs. Verifier keeps existing owning-ref checks by default; only arguments annotated with __nonown_allowed bypass MEM_ALLOC/ref_obj_id checks and then follow the same list-node validation path. Signed-off-by: Kaitao Cheng <[email protected]> Reviewed-by: Eduard Zingerman <[email protected]> --- Documentation/bpf/kfuncs.rst | 22 ++++++++++++++++++++-- kernel/bpf/verifier.c | 13 +++++++++++++ 2 files changed, 33 insertions(+), 2 deletions(-) diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 75e6c078e0e7..3a9db1108b95 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -207,8 +207,26 @@ Here, the buffer may be NULL. If the buffer is not NULL, it must be at least buffer__szk bytes in size. The kfunc is responsible for checking if the buffer is NULL before using it. -2.3.5 __str Annotation ----------------------------- +2.3.5 __nonown_allowed Annotation +--------------------------------- + +This annotation is used to indicate that the parameter may be a non-owning reference. + +An example is given below:: + + __bpf_kfunc int bpf_list_add(..., struct bpf_list_node + *prev__nonown_allowed, ...) + { + ... + } + +For the ``prev__nonown_allowed`` parameter (resolved as ``KF_ARG_PTR_TO_LIST_NODE``), +suffix ``__nonown_allowed`` retains the usual owning-pointer rules and also +permits a non-owning reference with no ref_obj_id (e.g. the return value of +bpf_list_front() / bpf_list_back()). + +2.3.6 __str Annotation +---------------------- This annotation is used to indicate that the argument is a constant string. An example is given below:: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8dd79b735a69..f3cf8d85bea0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10714,6 +10714,11 @@ static bool is_kfunc_arg_nullable(const struct btf *btf, const struct btf_param return btf_param_match_suffix(btf, arg, "__nullable"); } +static bool is_kfunc_arg_nonown_allowed(const struct btf *btf, const struct btf_param *arg) +{ + return btf_param_match_suffix(btf, arg, "__nonown_allowed"); +} + static bool is_kfunc_arg_const_str(const struct btf *btf, const struct btf_param *arg) { return btf_param_match_suffix(btf, arg, "__str"); @@ -12244,6 +12249,13 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ return ret; break; case KF_ARG_PTR_TO_LIST_NODE: + if (is_kfunc_arg_nonown_allowed(btf, &args[i]) && + type_is_non_owning_ref(reg->type) && !reg->ref_obj_id) { + /* Allow bpf_list_front/back return value for + * __nonown_allowed list-node arguments. + */ + goto check_ok; + } if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) { verbose(env, "%s expected pointer to allocated object\n", reg_arg_name(env, argno)); @@ -12253,6 +12265,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ verbose(env, "allocated object must be referenced\n"); return -EINVAL; } +check_ok: ret = process_kf_arg_ptr_to_list_node(env, reg, argno, meta); if (ret < 0) return ret; -- 2.50.1 (Apple Git-155)
